1. Field of the Invention
This invention relates generally to microprocessor systems and more particularly, to microprocessor systems having first and second read paths and first and second write paths and buffers to isolate the first and second read paths and the first and second write paths.
2. Discussion of the Related Art
The semiconductor industry is increasingly characterized by a growing trend toward fabricating more circuits on a given semiconductor chip. In addition, the circuits are more complex in order to provide the higher performance required by end users of the semiconductor chips. To achieve the higher performance demanded by the end users it is necessary to not only provide more complexity in the circuits and functions, but also to ensure that the circuits are smaller and faster. This is being achieved not only by reducing the size of individual devices but by placing the circuits closer together. In turn, this means that more circuits have to be interconnected. The method of interconnection must not detract from the performance and speed of the various functions on the semiconductor chip.
An interconnect provides a path or a medium for an electrical signal that is delivered from a source device to a destination or load device as illustrated in FIG. 1, in which CPU 12 is a source device when writing to a load device such as PIC 24, SCU 26, or MCU 28, for example. The interconnect 40 connects CPU 40 to the load devices. As shown in FIG. 1 there are usually more than one load device physically connected to the same interconnect.
One of the major problems associated with an interconnect is that the passage of an electrical signal through an interconnect takes time which, in turn, depends upon how much capacitance is present in the interconnect. The capacitance relates to the amount of electrical charge that needs to be added to or taken out from the interconnect as the source voltage changes from a low to high or from a high to a low. The amount of charge depends upon the width and length of the interconnect as well as on the interconnects distance from other signal interconnects and power paths. Additionally, the input nodes of any load or distribution device also add to the capacitance load. These capacitance loads are generally higher than interconnect capacitance loads. When many loads are connected to the same electrical point, all the capacitances together become formidable for a driver device, which slows down signal transitions, both from one point to another and from one value to another. The net result is that more time is required for signal transitions which detracts upon device performance and speed.
This invention is a solution to this problem and is accomplished by physically isolating the bigger capacitance loads. The devices used for the isolation are multiplexors (muxes) and buffers. The muxes help to keep the capacitive loads of the driver ports separated and in this way signals from an active driver is not impeded by the capacitive loads for non-active drivers. The buffers, on the other hand, isolate the capacitive loads of branches from the main trunk. As a result, the signals through the main trunk moves faster but still get transmitted to the branches. This ensures that regardless of how many branches there are, the signal transition times on the main trunk is not influenced the number of branches.